The numerical simulation is implemented by the Discrete Element Method[1]}. The particles are subjected to the contact forces, lubrication forces, and drag forces, and their displacements are calculated by
\(m_{i}\frac{d^{2}{r}_{i}}{dt^2}=\sum _{k}f_{n}^{ik}{n}^{ik}+\sum _{j}{f}_{ij}^{lubr,n}+\sum _{j}{f}_{ij}^{lubr,t}+ {f}_{i}^{drag}\) 
\({I}_{i}\frac{d{w}_{i}}{dt}=\sum _{k}f_{t}^{ik}{t}^{ik}\times {c}^{ik}+\sum _{j}{f}_{ij}^{lubr,t}\times {{c}}^{ij}\) 
